This invention relates to a treating device to be used in fabrication processes of, e.g., semiconductor devices.
A conventional treating device will be explained by means of a vertical heat treating device used in fabricating processes of semiconductor devices. In the vertical heat treating device semiconductor wafers to be treated are loaded on a wafer boat into a vertical process tube as a treatment chamber from below, and the interior of the process tube is heated under ambient atmosphere of set treatment gases to subject the semiconductor wafers to various treatments.
The vertical heat treating device of this type is used in, e.g., forming oxide films on semiconductor wafers, forming thin films by heat CVD, and forming heavily doped regions by heat diffusion.
FIG. 2 is a vertical sectional view of the conventional vertical heat treating device which schematically shows the structure thereof.
As shown in FIG. 2, the treatment chamber is provided by the process tube 1. The process tube 1 is a vessel of reverse U-shaped vertical section formed of, e.g., quartz. That is, the process tube 1 has a vertical cylindrical shaped having the top closed. A heater 2 is provided around the outside circumferential wall of the process tube 1.
A manifold 3 is connected to the lower end portion of the process tube 1. In the circumferential wall of the manifold 3 there are provided a gas feed pipe 5 for feeding fresh treatment gases into the process tube, and an exhaust pipe 4 for discharging gas from the process tube 2.
In a load lock chamber 11 directly below the manifold 3, a wafer boat 6 with a flange 6a is disposed vertically movably by a boat elevator 7. The wafer boat 6 holds a plurality (e.g., 120 sheets) of semiconductor wafers W on a plurality of vertically spaced shelves. The wafer boat 1 is lifted into and lowered out of the process tube 1 by the boat elevator 7. When the wafer boat 6 is lifted into the process tube 1, the flange 6a on the lower end of the wafer boat 6 closes the lower end of the manifold 3 to make the interior of the process tube 1 tightly closed. FIG. 2 shows a situation of the wafer boat lowered out of the process tube 1.
In this vertical heat treating device, semiconductor wafers W to be treated are held on the wafer boat 6, and the wafer boat holding the semiconductor wafers is lifted into the process tube 1 as the treatment chamber by the boat elevator 7 and closes the interior of the process tube 1 by the flange 6a. In this state, ambient atmospheric gas in the process tube 1 is evacuated through the exhaust pipe 4 to exhaust the gas, and when the interior of the process tube 1 reaches a set vacuum degree, set treatment gases are fed into the process tube through the gas feed pipe 5 and heated by the heater to subject the semiconductor wafers to required treatment.
In such treatment operation of semiconductor wafers, when the semiconductor wafers W are lifted on the wafer boat 6 into the process tube 1, or when the semiconductor wafers W is lowered out of the process tube 1 after a treatment, the semiconductor wafers W are placed in considerably high temperature ambient atmosphere on their way to and from the process tube 1. Accordingly it is a problem that if air is present there, natural oxide films are adversely formed on the surfaces of the semiconductor wafers W by O.sub.2 in the air. In view of this, it is preferable that the load and unload of the wafer boat 6 is conducted in the closed system structure (separated from atmospheric air) in ambient atmosphere of inert gas (non-oxygen atmosphere), such as N.sub.2 gas or others.
To give the device a closed system structure, a tightly sealed load lock chamber 11 is provided continuously on the lower end of the manifold 3 on the lower portion of the process tube 1 as the treatment chamber. In the load lock chamber 11, the wafer boat 6 and the boat elevator 7 are housed. A gas feed pipe 12 for feeding N.sub.2 gas as gas feeding means is provided in an upper portion of the load lock chamber 11, and an exhaust pipe 13 is provided in a lower portion of the load lock chamber 11.
A vacuum chamber 15 is connected to the load lock chamber 11 through a gate valve 14. A wafer carrier 17 can be inserted into and out of the vacuum chamber 15 through an outside shutter 16 by a lift mechanism 10. In the vacuum chamber 15 there is provided a carrier mechanism (robot) for conveying the semiconductor wafers W housed in the wafer carrier 17 into or out of the wafer boat 6 in the load lock chamber 11 through the gate valve 14. The vacuum chamber 15 is also provided with a gas feed pipe 19 for feeding N.sub.2 gas in the top thereof and an exhaust pipe 20 in the bottom thereof.
In such closed system structure vertical heat treating device, gas in the load lock chamber 11 is once evacuated through the exhaust pipe 13, and then N.sub.2 gas is fed through the gas feed pipe 12 to fill the load lock chamber 11 and the process tube 1. On the other hand the wafer carrier 17 is inserted into the vacuum chamber 15 through the outside shutter, and next the vacuum chamber 15 is evacuated through the exhaust pipe 20 to replace atmospheric air therein with N.sub.2 gas. Then N.sub.2 gas is fed into the vacuum chamber 15 through the gas feed pipe 19.
In this state, the semiconductor wafers W are conveyed by a convey mechanism 18 from the wafer carrier 17 in the vacuum chamber 15 to the wafer boat 6 in the load lock chamber 11 through the gate valve 14. Then the wafer boat 6 is lifted by the boat elevator 7 into the process tube 1, while the interior of the process tube 1 is tightly closed by the flange 6a.
After the semiconductor devices W are thus loaded into the process tube in N.sub.2 gas ambient atmosphere, N.sub.2 gas in the process tube 1 is discharged in the same way as above to be replaced by the set treatment gas, and the semiconductor wafers W are subjected to a required treatment. After this treatment, the treatment gas in the process tube 1 is evacuated through the discharge pipe 4, and instead N.sub.2 gas is fed through the gas feed pipe 5 to purge the interior of the process tube 1.
In this state the wafer boat 6 is lowered back into the load lock chamber 11 in N.sub.2 gas ambient atmosphere by the boat elevator 7, and the treated semiconductor wafers W are discharged through the gate valve 14 by the convey mechanism, 18 into the vacuum chamber 15.
In this arrangement, loading of the semiconductor wafers W into the process tube 1 from the vacuum chamber 15 through the load lock chamber 11, and unloading of the semiconductor wafers W from the process tube 1 along the reverse route can be conducted in ambient atmosphere of N.sub.2. The formation of natural oxide films on the semiconductor wafers W can be prevented.
But in this conventional vertical heat treating device of the closed system structure, as the treatment of semiconductor wafers is repeated, in the load lock chamber 11 in ambient atmosphere of an inert gas, such as N.sub.2 gas or others, gaseous impurities, such as carbon, are generated, or particles, such as oil mist, dust, etc., are generated, which results in decreases of purity of the inert gas in the load lock chamber 11. There are risks that these impurities may stick to the semiconductor wafers, or may cause chemical contamination, which causes deterioration of characteristics of semiconductor devices, and decreases of yields.
For the prevention of these causes, it is proposed that pure inert gas as the purge gas is incessantly supplied into the load lock chamber 11 through the gas feed pipe 12, while the inert gas in the load lock chamber 11 is exhausted outside together with impurities therein through the exhaust pipe 13, whereby ambient atmosphere of the inert gas in the load lock chamber 11 is kept at high purity. But this method needs flowing a large amount of inert gas, and uneconomically the gas consumption amount is large. Flow of a large amount of inert gas generate particles, and disadvantageously a larger amount of inert gas must be consumed for the removal of the particles.
In view of these problems, this invention has been made and provides a treating device which can maintain ambient atmosphere of inert gas in the load lock chamber at high purity with a minimum feed amount of the inert gas into the load lock chamber, and which is useful to suppress generation of particles and prevent chemical contamination.
To achieve this object, the treating device according to this invention is a treating device for conveying objects to be treated from a wafer boat waiting room into a treatment chamber to subject the objects to be treated to a required treatment, which comprises feeding means for feeding inert gas into the wafer boat waiting room, and retaining an ambient gas atmospheric pressure in the interior of the wafer boat waiting room at a suitable pressure, and gas circulating cleaning system including outlet means for letting out the inert gas from the wafer boat waiting room, a gas cleaning filter for removing gaseous impurity and particulate impurities in the let out inert gas, and return means for returning cleaned inert gas into the wafer boat waiting room.
In the treating device of this structure, inert gas is fed into the load lock chamber by gas feeding means, and an ambient atmospheric pressure of the inert gas in the load lock chamber is retained suitable, and on the other hand the inert gas in the load lock chamber is let out by the gas circulating cleaning system to have gaseous impurity and particulate impurities in the let out gas removed by the gas cleaning filter, and the cleaned inert gas is returned into the load lock chamber. That is, the inert gas in the load lock chamber is repeatedly cleaned and recirculated by the gas circulating cleaning device. Even with treating operations of objects to be treated repeated, the inert gas ambient atmosphere in the load lock chamber can be retained at high purity, and a supply amount of the inert gas into the load lock chamber can be small, which contributes to suppression of generation of particles and preclusion of chemical contamination.